1. Field of the Invention
This invention relates to a process for producing a foundry exothermic body.
2. Description of the Prior Art
A number of processes are available for making shaped foundry exothermic bodies from a raw material consisting of a mixture of an exothermic material, typically aluminum, an oxidant, typically manganese dioxide, a pro-oxidant, typically powdered cryolite, and a refractory as an aggregate. These include the commonly used hand ramming process, CO.sub.2 process and cold box process. For reasons explained below, however, the shell molding process is not used to produce shaped foundry exothermic bodies.
Among processes for making molds for metal casting, the shell molding process is the one that uses a foundry sand such as silica sand as the mold material. For example, a mold material referred to as "resin coated sand" is used which consists of silica sand coated with a thermosetting resin such as phenol resin as a binder. However, the raw material of a foundry exothermic body does not consist solely of refractory materials. It is a mixture also including materials with properties different from those of a refractory, such as the aforesaid exothermic material, typically aluminum, oxidant, typically manganese dioxide, pro-oxidant, typically powdered cryolite, and the like.
When the shell molding process is applied to form a foundry exothermic body using such a mixture as the forming material, the thermosetting resin added as binder must be coated on the forming material in order to minimize the amount thereof added and prevent its segregation. Since the properties of the components making up the mixture are extremely different, however, it is difficult to uniformly disperse the thermosetting resin used as binder in the raw material, In addition, when the coating with the thermosetting resin is effected by the hot process, which involves heating to around 130-160.degree. C., the raw material mixture may ignite and burn during the heating owing to reactions among the exothermic material, the oxidant and the pro-oxidant. This makes it difficult to supply a raw material mixture of constant composition on an industrial basis. Stable production of foundry exothermic bodies having prescribed uniform strength and exothermic property has therefore been difficult.